1. Field of the Invention
This invention relates to an electronic clinical thermometer, of approximately the same size as a mercury thermometer and having a water-tight casing, for sensing body temperature electronically and for displaying the temperature in digital form.
2. Description of the Prior Art
An electronic clinical thermometer typically comprises a temperature sensing element which converts body temperature information into an electric signal, a measuring unit for converting the electric signal from the temperature sensing element into a digital signal, an arithmetic unit for computing body temperature from the digital signal, a display unit for displaying the temperature computed by the arithmetic unit, a battery for supplying the abovementioned components with electric power, and a plastic casing for housing these components.
With the miniaturization of LSIs and other electronic components, circuit techniques have made it possible to achieve a significant reduction in the size of electronic clinical thermometers of the foregoing type. When such thermometers are used at institutions such as hospitals and clinics, a treatment such as sterilization or washing of the outer surface of the thermometer is essential in order to prevent the transmission of infection among patients through the medium of the thermometer. Clinical electronic thermometers having a watertight structure which permits such sterilization and washing are now available.
Since the casing of an electronic thermometer includes a number of joints at the location of such parts as a transparent plastic display window through which body temperature is read and a metal cap situated at the tip of the thermometer, it is necessary that these joints be made watertight in order to realize a waterproof structure. To this end, the inventor has succeeded in integrally molding such portions as the display window with the casing proper by a multiple-color injection molding technique, thereby obtaining a perfect waterproof property at these portions. However, achieving a waterproof condition at the temperature sensing tip of the thermometer covered by the metal cap has presented problems. Specifically, the conventional metal cap is attached to the extended, slender tip of the casing by using an adhesive. Since the adhesive cannot be applied evenly and smoothly between the metal cap and the casing, local gaps are formed that allow aqueous solutions to flow into or infiltrate the interior of the casing owing to such phenomena as capillary action. Furthermore, the metal cap tends to separate from the adhesive due to thermal expansion and contraction of the adhesive caused by changes in the outside temperature. This allows aqueous solutions to seep in through small voids which develop between the adhesive and cap.
The foregoing inflow or infiltration of aqueous solutions results in the moisture-induced malfunction of, e.g., a thermistor serving as the thermometer temperature sensor. Another drawback is the trouble involved in assembling the thermometer owing to use of the adhesive.